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January 27, 2012

This week's picks

Promiscuous mating produces offspring with higher lifetime fitness
"adult male offspring sired via extra-pair matings are more likely to sire extra-pair offspring (EPO) themselves... female EPO [extra-pair offspring, as in "that CEO is a real EPO"] benefited primarily through enhanced fecundity"

Repeatability and Contingency in the Evolution of a Key Innovation in Phage Lambda

The take-it-or-leave-it option allows small penalties to overcome social dilemmas

Mothers modify eggs into shields to protect offspring from parasitism

Reconciling long-term cultural diversity and short-term collective social behavior

A micro-geography of fear: learning to eavesdrop on alarm calls of neighbouring heterospecifics
"superb fairy-wrens... fled to cover to playback of noisy miner,,, alarm calls only in locations where miners were present [Australians sure know how to name birds!]"

The peopling of Europe and the cautionary tale of Y chromosome lineage R-M269 "existing data and tools are insufficient to make credible estimates for the age of this haplogroup"

January 23, 2012

Does our recent work "prove evolution"?

Many aspects of evolution are already well understood. We have more data on recent events (the last 100 million years or so) than on ancient ones. For example, when was the last time anyone offered a detailed arguement that molecular data on humans and chimps are more consistent with independent creation than with evolution from a common ancestor? But we have much less information about the origin of life and (a billion or so years later), the evolution of multicellular life from unicellular ancestors.

There are thousands of papers on how natural selection and other processes change species over generations, and thousands more on how species split into more species, but far fewer on major transitions: genes uniting into chromosomes, the origin of eukaryotes, multicellularity, and so on. There are even fewer attempts to study such transitions under controlled, repeatable conditions. That's why our recent paper has generated so much interest -- not because it sheds any light on how life arose in the first place.

But some creationist is criticizing our recent paper, on You-Tube. He points out that we used centrifugation -- the lowest setting, but still much stronger than gravity -- to select for multicellularity. If such strong gravitational forces were the only way multicellularity could evolve by natural selection, then we would indeed have to look for other explanations. But regular gravity works, too; it just takes longer. (Longer settling time per selection cycle, not necessarily more cycles.) So does predation, as shown by Boraas et al. in 1998. Certain economies of scale might work, as suggested recently by Koschwanez et al. And resistance to stresses like UV might work, too, as I suggested in an earlier post.

We aren't so much asking what natural forces could select for multicellularity (protection from predators versus UV, say), but focusing on questions like:
* Given strong selection, how fast can multicellularity evolve? (fast! so why did it take billions of years?)
* What genetic changes are key to the initial transition -- are there multiple genetic routes to multicellularity? -- and what further changes occur early in multicellular evolution? (in progress)

To answer the latter sorts of questions, it helps to be able to apply exactly the same selection pressure to multiple replicate populations -- we've used ten -- and that's easier with centrifugation than with finicky predators.

Unlike us, Jesus isn't around to object that "that wasn't what I said." So I do want to point out an apparent misattribution in the You-Tube video:

"Jesus was right about creation, 2000 years ago. I wonder what else he was right about." -- creationist on U-tube

If Jesus said anything much about creation, I missed it, but there's this:
And when thou prayest, thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward. But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly. -- Matthew 6:5-6

And God supposedly said something about not bearing false witness. Surely attributing things to Jesus that he never said would qualify.

January 20, 2012

Also this week...

Variation in cognitive functioning as a refined approach to comparing aging across countries "The degree to which demographic aging translates into societal challenges depends to a considerable extent on the age at which mental functioning becomes signi´Čücantly impaired.... In several countries with older populations, we find better cognitive performance on the part of populations aged 50+ than in countries with chronologically younger populations."

Large-scale, spatially-explicit test of the refuge strategy for delaying [sprayed] insecticide resistance
"refuges delayed resistance and treated cotton fields accelerated resistance"

The evolutionary basis of human social learning "We tested nine hypotheses derived from theoretical models, running a series of experiments..."

Collaborative learning in networks "In contrast to prior work, however, we found that efficient networks outperformed inefficient [slower] networks, even in a problem space with qualitative properties thought to favor inefficient networks."

Historical contingency affects signaling strategies and competitive abilities in evolving populations of simulated robots "populations with the more complex [but less efficient] strategy outperformed the populations with the less complex strategy"

The spread of a transposon insertion in Rec8 is associated with obligate asexuality in Daphnia "this element may be in the process of spreading through the species"

January 17, 2012

Experimental evolution of multicellularity: the movies

In case you missed the news coverage by Carl Zimmer in the New York Times, Jeff Akst in The Scientist, and Ed Yong on Nature's news site, among others, our paper on experimental evolution of multicellularity has just been published in Proceedings of the National Academy of Sciences. It's open access, so you can read all the details yourself.

In nature, multicellularity has only evolved a few about 25 times, and it took billions of years. But Mike Travisano (a fellow faculty member in Ecology Evolution and Behavior) and postdoc Will Ratcliff (who earned a PhD with me recently) came up with a simple and repeatable way to speed the process enough to study under lab conditions: selection for rapid settling in liquid media, starting with unicellular yeast. They kindly invited Mark Borrello and me to participate in this exciting project, which also depended on hard work by undergrads Kristin Jacobsen, Mitch Hoverman, and Amanda Muehlbauer and funding from the National Science Foundation. We have also had some support for preliminary genetic analysis (in progress) from the College of Biological Sciences at the University of Minnesota.

The best collection of links related to this work is at the Microbial Population Biology (Micropop) website, which brings together people and projects from the laboratories of Mike Travisano, Tony Dean, and me. I particularly recommend the videos showing reproduction of snowflake-like multicellular yeast via smaller multicellular propagules -- think of plants reproducing from fragments, rather than seeds -- and genetic stability of the multicellular trait, shown by regrowth of multicellular clusters from enzymatically isolated single cells.

I gave some background for this work in an earlier post, when Elizabeth Pennisi wrote about it for Science.

Update: two scientists criticize some of our claims, and Will Ratcliff responds, on Carl Zimmer's blog, here.

January 12, 2012

Flycatchers use early birds (great tits) to crowd-source clutch size

A bird that tries to raise too many chicks this year may not survive to reproduce again. So there's a tradeoff between current and future reproduction. Earlier, I discussed how stress hormones over-worked mothers pass to their chicks decrease survival of this year's chicks, whereas the reduced work-load can increase the mother's life-long reproduction. But how many chicks is too many? It depends on food supply and other conditions that vary from year to year.

Rather than researching conditions themselves, flycatchers could wait to see how many eggs other flycatchers lay. This is the approach many humans use to decide how much to invest in stocks, but it doesn't work any better for the flycatchers than it does for us. By the time they figure out what others are doing, it's too late to take advantage of the information.

An alternative crowd-sourcing approach is to see how many eggs were laid by another species of bird that finishes egg-laying a bit earlier. Indeed, Jukka Forsman and colleagues report, in a recent paper in Biology Letters, that "Observed heterospecific clutch size can affect offspring investment decisions."

They placed simulated great-tit nests, containing either 4 or 13 imitation eggs, near likely nesting sites for flycatchers. Older flycatchers near 4-egg fake nests laid an average of 10.4 grams of eggs, while those near 13-egg nests laid 11.5 grams of eggs, about 10% more. The increase was partly due to laying more eggs and partly due to laying heavier eggs. Younger know-it-alls were less influenced by the imitation nests.

The direction of the change in investment in current-year reproduction is consistent with the hypothesis that flycatchers rely on clutch size of great tits as one measure of their own optimal clutch size for this year's conditions. But a 10% change seems too small a response to 13 eggs versus 4, assuming the great tits know what they're doing. Then again, conditions change over the season, so relying 100% on what an earlier species did would be risky.

Also, this year's conditions aren't all that matters. I have explained earlier that, to maximize one's proportional genetic representation in future generations, it can be better to produce one offspring this year than two next year (if the population is increasing), but it can also be better to produce one offspring next year than two this year (if the population is decreasing). So, ideally, bird decisions about reproductive investment should be based on predicted population trends, not just maximizing the lifetime number of chicks fledged.

January 6, 2012

This week's picks

Experimental litter size reduction reveals costs of gestation and delayed effects on offspring in a viviparous lizard

Genetic adaptation to captivity can occur in a single generation

Ancestral Developmental Potential Facilitates Parallel Evolution in Ants

Common mechanism underlies repeated evolution of extreme pollution tolerance

Unravelling transmission trees of infectious diseases by combining genetic and epidemiological data

Genetic code translation displays a linear trade-off between efficiency and accuracy of tRNA selection

Male attractiveness regulates daughter fecundity non-genetically via maternal investment

Social learning spreads knowledge about dangerous humans among American crows

Fitness Trade-Offs and Environmentally Induced Mutation Buffering in Isogenic C. elegans

January 4, 2012

Pre-order "Darwinian Agriculture"

Amazon.UK has been listing my book for a while and now says it's #5 in Crop Production and #6 in Biotechnology, based on pre-orders. Order from them and maybe you can help it overtake The Cannabis Grow Bible for third place.

Oops! Biomimicry just leap-frogged past Darwinian Agriculture with a Kindle edition, to take #1 in Biotechnology, somehow bumping Darwinian Agriculture to #10 (just ahead of Little Book of Beer Tips).

You can also order from Amazon.com in the US or direct from Princeton University Press.

Link to Carnival of Evolution

When I started this blog, there were not many blogs discussing recent scientific papers in evolution. Now there are lots -- see this month's Carnival of Evolution -- so maybe I should move on to something else, like a narrower focus on evolutionary aspects of agriculture, once my book on Darwinian Agriculture comes out in July.